In computer applications, a number of multi-chip modules (MCM) may be interconnected by using a through-hole interconnector. High performance computers require the interconnection of a large number of MCMs by an interconnector which can facilitate the passage of electrical signals at a high rate of speed. In order to accommodate such a large number of MCMs and the desired rate of signal transfer, the interconnectors must be manufactured having precise dimensions and tolerances. The precise tolerances of the interconnector are required to ensure the connection and efficient passage of the electrical signal through the interconnector to and from the MCM. The most important interconnector dimension and tolerance is that of the electrical interconnects. The electrical interconnects are the electrically conductive portion of the conductor which mates with the MCM and facilitates the transfer of electrical signals.
Through-hole interconnectors used in the art are commonly made from a dielectric material such as plastic or rubber and the like comprising a conductive portion, i.e., electrical interconnects, to accommodate the MCM. Interconnectors made from such dielectric materials, because of their flexible construction, are not rigid enough to permit their use in high performance computer applications where precise dimensions and tolerances are required. The use of such a flexible interconnector can result in the improper alignment and mating of the electrical interconnects with MCMs, circuit boards, or integrated circuit devices. Additionally, such flexible interconnectors are unable to maintain their dimensional integrity under conditions of applied force. The applied forces may be the result of either thermal stresses, caused by thermal cycling, or by the use of pressure contacts.
The electrical connection between the interconnector and the MCM or circuit board is generally made by solder joint, soldering the electrically conductive portion of the MCM or circuit board to the interconnector's complementary electrical interconnects. This method of joining the interconnector and MCM or circuit board requires that the solder joint be melted in order to separate the two members. The need to melt the solder joint in order to remove a single failed MCM or circuit board from a interconnector may not be practical in an application such as a high performance computer where the failed MCM or circuit board may be difficult to access due the proximity of surrounding MCMs or circuit boards.
The advent of high performance computers creates a greater need for interconnectors that are capable of accommodating a large number of components, i.e., MCMs, integrated circuits, circuit boards and the like, (high-density interconnector). The interconnector should also accommodate such components in a manner which maximizes both the electrical conductivity between the interconnector and the connecting electrical component, and the mechanical reliability of the electrical connection, so as to facilitate the rapid transfer of electrical signals through the interconnector.
High density through-hole interconnectors are known in the art. Such interconnectors are capable of accommodating multiple components by the nature of their construction, namely, a dielectric substrate comprising a plurality of electrical interconnects. Such interconnectors are manufactured by forming a plurality of holes through the dielectric substrate and subsequently filling the holes with an electrically conductive material. The filled holes form the electrical interconnect and are characterized by their aspect ratio, defined as the depth or length of the electrical interconnect divided by the diameter of the electrical interconnect. In order to accommodate the increased circuit density of integrated circuits used in computer construction, it is desirable that the interconnector possess a large number of electrical interconnects, or have a high electrical interconnect density.
An interconnector comprising electrical interconnects having a high aspect ratio allows for a greater number of electrical interconnects per a given interconnector (high density), and thereby allows the interconnector to accommodate a larger number of MCMs, integrated circuits, circuit boards and the like.
Interconnectors with electrical interconnects having a high aspect ratio are known in the art. Such interconnectors are manufactured by the method of forming a dielectric substrate of given thickness and then forming a pattern of holes by methods well known in the art such as drilling, punching, chemical etching and the like. The holes then filled with an electrically conductive material (metalized) to form the electrical interconnect. Interconnectors manufactured according to this method comprise electrical interconnects having an aspect ratio up to about two. In order to accommodate the circuit density of integrated circuits used in the construction of high powered computers it is desired that the interconnector comprise electrical interconnects having an aspect ratio greater than about four.
Through-hole interconnectors with electrical interconnects having an aspect ratio greater than about two are difficult to manufacture according to known methods because the through hole forming tool must necessarily be relatively long and narrow, making it unstable and difficult to control during the hole forming step. During the hole forming process, the inherent instability of using such a tool either causes the deformation or misalignment of the hole or causes the tool to break. The difficulty of forming interconnector through holes using such known methods effectively limits the ability to obtain electrical interconnects having aspect ratios greater than about two.
Through-hole interconnectors must also facilitate the high speed transfer of electrical signals to and from the integrated circuit or other electrical component that it is connected to. The electrical interconnects should, therefore, be constructed so that they have low resistance and have good electrical conductivity. According to known methods, electrical interconnects are typically formed by filling the pattern of holes made in the dielectric substrate by flowing a molten conductive material into the hole (metalizing). As the dimensions of the hole become smaller for greater circuit densities, and as the aspect ratio increases, the molten conductive material flowing into the hole begins to deposit about the inner wall of the hole. As the conductive material deposited about the wall of the hole solidifies, it acts to reduce the diameter of the hole, and thereby inhibits further flow of the molten conductive material down into the hole. As the diameter progressively decreases during the filling process, the through hole eventually becomes sealed at both ends, thereby creating a void in the center of the hole. Since these voids by definition lack conductive material, their presence causes high resistance areas in the electric interconnect which in turn may result in the improper operation of an electrical component connected to the interconnector.
The method of filling the through holes with molten conductive material (metalization) also limits the materials which can be used to either metals or alloys of metals. Metal-nonmetal compositions can not be used. Generally speaking, metals are desirable electrical connectors because of their high electrical conductivity. However, metals also have thermal expansion characteristics that are different (typically higher) than that of dielectric material. In the construction of interconnectors it is desirable that the material selected for the electrical interconnect have thermal expansion characteristics similar to or matching that of the surrounding dielectric substrate and the integrated circuit or other electrical components that it will connect with. The ability to match coefficients of thermal expansion is desirable because differences in thermal expansion characteristics between connected components cause thermal stresses to develop between them which may eventually lead to reliability problems in their connection, ultimately resulting in mechanical failure.
It is, therefore, desirable that through-hole interconnectors used in the construction of high performance computers have precise dimensions in order to facilitate the accurate placement of MCMs, integrated circuits, circuit boards and the like. It is also desirable that the interconnector be constructed with electrical interconnects having a high aspect ratio, thus allowing the interconnector to accommodate integrated circuits and the like having high circuit densities. It is desirable that the interconnector be capable of employing various contact schemes, but particularly, one which would permit easy configuration changes. It is also desirable that the method of manufacturing such high density interconnectors be both practical and economically feasible.
It is desirable that the interconnector be manufacture with electrical interconnects having a high electrical conductivity and low resistance to facilitate the rapid transfer of electrical signals. It is also desirable that the interconnector be constructed with electrical interconnects having thermal expansion characteristics similar to those of the nonconductive interconnector substrate and the integrated circuits or electrical components that it will connect with.